R Agricola1, J H Waarsing2, G E Thomas3, A J Carr4, M Reijman5, S M A Bierma-Zeinstra6, S Glyn-Jones7, H Weinans8, N K Arden9. 1. Department of Orthopaedics, Erasmus MC University Medical Centre, Rotterdam, The Netherlands. Electronic address: r.agricola@erasmusmc.nl. 2. Department of Orthopaedics, Erasmus MC University Medical Centre, Rotterdam, The Netherlands. Electronic address: e.waarsing@erasmusmc.nl. 3. Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, NIHR Musculoskeletal Biomedical Research Unit, University of Oxford, Nuffield Orthopaedic Centre, Oxford, England, UK. Electronic address: geraint.thomas@ndorms.ox.ac.uk. 4. Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, NIHR Musculoskeletal Biomedical Research Unit, University of Oxford, Nuffield Orthopaedic Centre, Oxford, England, UK. Electronic address: andrew.carr@ndorms.ox.ac.uk. 5. Department of Orthopaedics, Erasmus MC University Medical Centre, Rotterdam, The Netherlands. Electronic address: m.reijman@erasmusmc.nl. 6. Department of Orthopaedics, Erasmus MC University Medical Centre, Rotterdam, The Netherlands; Department of General Practice, Erasmus MC University Medical Centre, Rotterdam, The Netherlands. Electronic address: s.bierma-zeinstra@erasmusmc.nl. 7. Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, NIHR Musculoskeletal Biomedical Research Unit, University of Oxford, Nuffield Orthopaedic Centre, Oxford, England, UK. Electronic address: sion.glyn-jones@ndorms.ox.ac.uk. 8. Department of Orthopaedics, Erasmus MC University Medical Centre, Rotterdam, The Netherlands; Department of Biomechanical Engineering, Delft University of Technology, Delft, The Netherlands; Department of Orthopaedics and Rheumatology, University Medical Centre Utrecht, Utrecht, The Netherlands. Electronic address: h.h.weinans@umcutrecht.nl. 9. Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, NIHR Musculoskeletal Biomedical Research Unit, University of Oxford, Nuffield Orthopaedic Centre, Oxford, England, UK. Electronic address: nigel.arden@ndorms.ox.ac.uk.
Abstract
INTRODUCTION: Cam impingement is characterized by abnormal contact between the proximal femur and acetabulum caused by a non-spherical femoral head, known as a cam deformity. A cam deformity is usually quantified by the alpha angle; greater alpha angles substantially increase the risk for osteoarthritis (OA). However, there is no consensus on which alpha angle threshold to use to define the presence of a cam deformity. AIM: To determine alpha angle thresholds that define the presence of a cam deformity and a pathological cam deformity based on development of OA. METHODS: Data from both the prospective CHECK cohort of 1002 individuals (45-65 years) and the prospective population-based Chingford cohort of 1003 women (45-64 years) with respective follow-up times of 5 and 19 years were combined. The alpha angle was measured at baseline on anteroposterior radiographs, from which a threshold for the presence of a cam deformity was determined based on its distribution. Further, a pathological alpha angle threshold was determined based on the highest discriminative ability for development of end-stage OA at follow-up. RESULTS: A definite bimodal distribution of the alpha angle was found in both cohorts with a normal distribution up to 60°, indicating a clear distinction between normal and abnormal alpha angles. A pathological threshold of 78° resulted in the maximum area under the ROC curve. CONCLUSION: Epidemiological data of two large cohorts shows a bimodal distribution of the alpha angle. Alpha angle thresholds of 60° to define the presence of a cam deformity and 78° for a pathological cam deformity are proposed.
INTRODUCTION:Cam impingement is characterized by abnormal contact between the proximal femur and acetabulum caused by a non-spherical femoral head, known as a camdeformity. A camdeformity is usually quantified by the alpha angle; greater alpha angles substantially increase the risk for osteoarthritis (OA). However, there is no consensus on which alpha angle threshold to use to define the presence of a camdeformity. AIM: To determine alpha angle thresholds that define the presence of a camdeformity and a pathological camdeformity based on development of OA. METHODS: Data from both the prospective CHECK cohort of 1002 individuals (45-65 years) and the prospective population-based Chingford cohort of 1003 women (45-64 years) with respective follow-up times of 5 and 19 years were combined. The alpha angle was measured at baseline on anteroposterior radiographs, from which a threshold for the presence of a camdeformity was determined based on its distribution. Further, a pathological alpha angle threshold was determined based on the highest discriminative ability for development of end-stage OA at follow-up. RESULTS: A definite bimodal distribution of the alpha angle was found in both cohorts with a normal distribution up to 60°, indicating a clear distinction between normal and abnormal alpha angles. A pathological threshold of 78° resulted in the maximum area under the ROC curve. CONCLUSION: Epidemiological data of two large cohorts shows a bimodal distribution of the alpha angle. Alpha angle thresholds of 60° to define the presence of a camdeformity and 78° for a pathological camdeformity are proposed.
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